JANET JACKSON floored everyone with her noticeable weight gain earlier in the year, but she revealed to ET how she lost the weight — and why she gained it in the first place.

"I put on the pounds for a film I was to do … which a lot of people didn’t know," Janet tells our KEVIN FRAZIER. "They wanted a full-figured woman."

Janet says they had to push the project back, and she had to pass on the opportunity in order to work on her new album. Of course, she had another assignment to take care of — losing the weight!

"I worked really hard, and I continue to work very hard," says Janet about her lean new look. "I have to give credit to my parents’ genes I suppose, and just working with great people [that] make me look good, and nutrition and a great trainer."

Janet’s fellow singer KELLY CLARKSON says she was proactive about staying healthy while on tour. As part of her diet plan, Kelly has gone cold turkey on sugary sodas and switched to vitamin water.

Being healthy is more important to Kelly than starving on the latest fad diet. The Texas-born singer, who grew up eating pizza and burritos and sipping sodas in her school cafeterias, lays no claim to being a skinny Minnie. She will be the first to admit, she is more interested in staying healthy than in squeezing into a size 0. So Kelly has hired a chef to create meals for her and her crew.

"She cooks anything," the first "American Idol" winner says. "It’s not like a diet or anything. It’s just good, organic, energy food."

By making changes to his diet and starting an exercise program, Kelly’s "Idol" counterpart RUBEN STUDDARD dropped nearly 100 pounds over the summer, and wants his fellow Alabamians to get into the weight-loss groove, too.

The Birmingham native has joined Scale Back Alabama, an eight-week weight-loss initiative that seeks to encourage the 25 percent of the residents in his home state who are obese to lose 10 pounds during the span of the campaign.

Ruben told the AP he wanted to get in shape "because I have a family history of diabetes and high blood pressure and things of that nature."

Meanwhile, "Family Ties" alum TINA YOTHERS turned to "Celebrity Fit Club" to help her lose her baby weight.

After giving birth, Tina tipped the scales at 210 pounds. She tells ET, "That was hard. That was really hard. You don’t realize as it’s coming on how big you’re getting."

Truth be told, the new mom was a size 18 when she began "Celebrity Fit Club," but after 100 days of diet and exercise, she is thinner than she has ever been!

"I’m a size six now," a proud Tina tells ET. "I’ve never been a six. Even when I did ‘Family Ties,’ I was a seven/eight."

And the always-gorgeous CARMEN ELECTRA even shares her secret for staying slim — a weight-loss beauty pill called NV, and she just happens to be the product’s spokesperson.

"Everything in the pill is natural," she says.

Carmen says that it’s a great way to stay healthy. "It replenishes everything you think you’ve taken out of your body when you’re working out and trying to lose weight."

And although Carmen takes great care of herself, she does admit to giving in to a hankering now and again. "I do crave pizza," she admits. "I’m still going to have that pizza!"

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